Lewis Hamilton steers his McLaren through the wet during the second practice session in Yeongam. Photograph: Saeed Khan/AFP/Getty Images

Lewis Hamilton topped the timings in Friday's second practice session ahead of the Korean Grand Prix, with both practice periods, the first headed by Michael Schumacher, conducted in wet conditions.

Hamilton was 0.104sec ahead of his team-mate Jenson Button with Sebastian Vettel, who took third place, a further 1.7sec adrift. The running may not be truly indicative of real race-pace despite McLaren's recent resurgence in form, as no dry laps were completed and the weather is expected to be dry on Saturday and Sunday.

There was almost no activity for the first hour of free practice one until the major players came out for the final 30 minutes. Hamilton posted the first quick time but was soon overtaken by Toro Rosso's Sébastien Buemi. The conditions remained very tricky on a wet and green track with numerous drivers struggling for grip, spinning or going off. Vettel, who ran wide on Turn 11, narrowly avoiding a wall, then did go quickest before Schumacher finished on top with a time of 2min 02.784sec.

Despite a relatively dry spell in between sessions, the cars resumed in the wet, this time looking to maximise track-time, going out from the off. The Red Bulls of Vettel and Mark Webber led the way but were soon surpassed by Hamilton and Button, swapping fastest times on intermediate tyres, with the rain reoccurring throughout.

Ferrari's Fernando Alonso made a spirited effort to take third from the Red Bull's only to see Vettel reclaim it in the final third of the session, but the world champion could manage only a lap of 1:52.646 to Hamilton's 1:50.828.

Mercedes's Nico Rosberg, who collided with Jaime Alguersuari while going wide on turn one as the Toro Rosso exited the pit lane during the second session, called for the pit exit in Yeongam to be redesigned. Rosberg lost his front wing in the incident.

"It would be worth reconsidering if the pit-exit couldn't be done a little bit differently," he said. "It was not great circumstances, it just all came together. He came out at the exact wrong moment."

He admitted he had mistimed his braking, causing him to go wide but that there would not have been contact if the exit did not rejoin the track at that point. "I just locked up a little bit. I couldn't have avoided him any more," he said. "I thought he was going to stop a little bit more to let me go through, but then he didn't and by the time I realised that, it was too late."